1. Field of the Invention
The present invention relates to an image processing apparatus and image processing method configured to combine image data for plural images picked up in time sequence.
2. Description of the Related Art
In recent years, image pickup apparatuses such as digital cameras equipped with a comparative bright combination processing function have been proposed. The comparative bright combination processing here involves a process of comparing pixel values at a same pixel position in plural images picked up in time sequence and replacing the pixel values at the pixel position with a larger pixel value.
The comparative bright combination processing is used for plural images picked up in time sequence at a necessary and sufficiently short shutter speed (so-called continuous shooting) in a photography scene containing a comparatively bright and small moving object and allows a trajectory of the moving object to be acquired as a good image with a high S/N ratio.
Some of photography scenes to which the comparative bright combination processing is applied include fireworks photography, astronomical photography, and photographing of moving headlight trajectories of a vehicle and the like at night.
For example, in the case of fireworks photography, a flow of bright spots making up fireworks lasting a few seconds are picked up in time sequence at a shutter speed shorter than the few seconds and plural images are acquired. Also, in the case of astronomical photography, very slow movements of stars on the celestial sphere are picked up in time sequence at a short shutter speed and plural images are acquired. Furthermore, in the case of moving headlight trajectories of a vehicle and the like at night, similarly the headlights are picked up in time sequence at a shutter speed shorter than a shutter speed corresponding to lengths of the moving trajectories to be photographed and plural images are acquired.
In any of the cases, if the plural images obtained are subjected to comparative bright combination, images with good S/N can be obtained by avoiding such image quality deterioration as will be caused by a dark current if a long shutter speed is used for photographing.
As such a technique, for example, Japanese Patent Application Laid-Open Publication No. 2014-212415 describes an image pickup apparatus equipped with a comparative bright combination processing section which repeats comparative bright combination processing each time new image data is acquired, where the comparative bright combination processing involves storing first image data as cumulative comparative bright combined image data, comparing newly acquired image data with the cumulative comparative bright combined image data on a pixel by pixel basis, and reorganizing the cumulative comparative bright combined image data using a larger pixel data as new pixel data.
Furthermore, Japanese Patent Application Laid-Open Publication No. 2014-212415 describes a technique which includes a comparative bright combination processing section and a comparative dark combination processing section, calculates differential image data between cumulative comparative bright combined image data and cumulative comparative dark combined image data, and combines together image data obtained by multiplying the cumulative comparative dark combined image data by a gain value and image data obtained by multiplying the differential image data by an arbitrary gain value.